Recurring to the principal features of the range between Mbale-mbale and Vandrani, one may remark the extensive occurrence of basic agglomerates and tuffs on both slopes, the prevalence of olivine-basalts, the frequency of the semi-vitreous and vitreous or rather pitchstone condition of these rocks, and their semi-ophitic character, especially on the summit and north slopes. From the vesicular structure of the rocks of the Koro-tini Bluff and from the character of its tuffs and agglomerates, it is to be inferred that they are the direct products of eruptions, probably in shallow seas. On the other hand, the tuffs (often foraminiferous) as well as the agglomerate-tuffs of the north and south slopes of the range are in part suggestive of marine erosion. Intrusive masses of basalt are to be observed occasionally, and doubtless to this cause may be attributed the concretionary structure of the tuffs in places, and the alteration of these deposits in one or two localities, where they are penetrated by cracks filled with chalcedony.
(3) TRAVERSE OF THE KORO-TINI RANGE FROM VATU-KAWA TO VANDRANI.—On leaving Vatu-kawa[69], which is not more than 50 feet above the sea, the ascent for the first 600 feet up the steep mountain-side lies along the rocky bed of the Wai-ni-ngio River, which from its rapid fall has more the character of a torrent. On its sides are exposed basic agglomerates and agglomerate-tuffs; whilst the large boulders in its bed are composed of a somewhat altered olivine-basalt. At 600 feet the track abandons the stream-course for the steep mountain slopes, and thence up to 1,100 feet similar agglomerates and tuffs prevail. At this last-named elevation there are displayed fine and coarse indurated palagonite-tuffs, a little altered in character and with little or no lime. A specimen of the former, of which the materials composing it do not exceed ·2 mm. in size, shows in the slide an occasional “Globigerina” test filled with palagonitic debris. Such a marine deposit is evidently not of shallow-water origin. The coarser tuff is made up of compacted sub-angular fragments, not over 2 mm. in size; but contains no organic remains. The prevailing rocks exposed between 1,100 and 1,900 feet, a little below the summit of the range, are somewhat altered compacted non-calcareous breccia-tuffs, composed of sub-angular fragments 5 or 6 mm. in size, of a more or less glassy and often vacuolar basic or basaltic andesite, only in part palagonitised, the vacuoles as well as the interstices between the fragments being sometimes filled with a zeolite.[70]